ELECTRIC CHARGES AND FIELDS QUESTION SERIES

Ø What is meant by quantization of electric charge? What is the cause of quantization of electric charge?

Ø  Can you ignore quantization of charge? If yes, under what conditions?

Ø Estimate the total number of electrons present in 100 g of water. How much is the total negative charge carried by these electrons? Avogadro’s number =6.02 x 10²³ and molecular mass of water=18.     [answer = 5.35 x 10⁶c]

Ø If a body gives out 10⁹ electrons every second, how much time is required to get a total charge of 1 c from it?  {answer= 198.18year}

Ø State the law of conservation of charge. Give some example to illustrate this law.

Ø State coulomb’s law in electrostatics. Express the same in SI units. Name and define the units of electric charge.

Ø Write coulomb’s law in vector form. What is the importance of expressing it in vector form?

Ø What is the range over which coulombian forces can act? State the limitations of coulomb’s law in electrostatics.

Ø What do mean by permittivity of a medium? Define dielectric constant in terms of forces between two charges.

Ø Give a comparison of the electrostatics and gravitational forces.

Ø State the principle of superposition of electrostatic forces. Hence write and expression for the force on a point charge due to a distribution of N-1 point charges in terms of their position vectors.

Ø NCERT- EXAMPLE-1.6 & 1.7

Ø Charges of + 5uq, +10uq and -10uq are placed in air at the corners A, B, and C of an equilateral triangle ABC, having each side of 5cm. determine the resultant force on the charge at A.  [180N,60⁰]

Ø Four equal point charges each of 16uc are placed on the four corners of a square of side 0.2m. Calculate the force on any one of the charges. [110.3N]

Ø Three point charges of +2uq, -3uq and -3uc are kept at the vertices A , B and C respectively of an equilateral triangle of side 20cm as shown in fig. what should be the sign and magnitude of the charge to be placed at the midpoint M of side BC so that the charge at A remains in equilibrium?

[3.9µC]

                                                                                

Ø  Four charges +q, +q, -q & -q are placed respectively at the four corners A, B, C and D of a square of side a. calculate the force on a charge Q placed at the centre of the square.

Ø Explain the concept of electric field. And write the unit and dimensions of electric field.

Ø What is physical significance of electric field? Find expression for electric field intensity due to a point charge.

Ø NCERT EXAMPLE PROBLEM 1.8 & 1.9.

Ø Calculate the electric field strength required to just support a water drop of mass 10^-3 kg and having a charge 1.6 x10^-19C.   [6.125 x 10^-19NC^-1]

Ø An electron moves a distance of 6 cm when accelerated from rest by an electric field of strength 2x10⁴NC^-1. Calculate the time of travel. The mass and charge of electron are 9 x 10^-31 C respectively.

Ø Calculate the voltage needed to balance an oil drop carrying 10 electrons when located between the plates of a capacitor which are 5mm apart. The mass of oil drop is        3 x 10^-16kg. Take g=10m/s^2.    [9.375v]

Ø An electron falls through a distance of 1.5cm in uniform electric fields of magnitude 2.0x 10⁴NC^-1. The direction of the field is reversed keeping its magnitude unchanged and a proton falls through the same distance. Compute the time of fall in each case. [ncert]